Graph Waveform Array VI1.12004/06/24 14:22:38 GMT-52004/07/16 15:15:54.748 GMT-5NationalInstrumentscertification@ni.comElizabethGregorylizzardg@rice.eduMalanShiralkarmshiralkar05@hotmail.comHarikaBasanailsai@rice.eduNationalInstrumentscertification@ni.comTo create an array by auto-indexing a For Loop and to plot the array on a waveform graph.
Complete the following steps to build a VI that generates and
plots an array on a waveform graph and modify the
VI to graph multiple plots.
Front Panel Open a blank VI and build the front panel shown in
.
Place an array, located on the
Controls>>All Controls>>Array &Cluster
palette, on the front panel.
Label the array Waveform Array.
Place a numeric indicator, located on the
Controls>>Numeric Indicators palette, in
the array shell.
Place a waveform graph, located on the
Controls>>Graph Indicators palette, on
the front panel.
Block Diagram Build the block diagram shown in .
Place the Thermometer VI on the block
diagram. Select Functions>>All Functions>>Select
a VI and navigate to C:\Exercises\ LabVIEW
Basics I\Thermometer.vi. This subVI returns one
temperature reading during each For Loop
iteration.
Use the (Demo) Thermometer VI if you do
not have a DAQ device available.
Place a For Loop, located on the
Functions>>All Functions>>Structures
palette, on the block diagram. In this exercise, each
For Loop iteration generates a temperature
value and stores it in the indexed tunnel. Create a
constant of 100 for the count terminal.
Wire the block diagram as shown in .
When you wire data to charts and graphs, refer to the
Context Help window for more information
about wiring the objects, including whether to use a
Build Array or Bundle
function, the order of the input terminals, and so
on. In general, use a waveform chart for
single scalar points, a waveform graph
for an array of y values, and an XY graph
for an array of
x values and an array of
y values. For example,
if you move the cursor over a waveform
graph terminal on the block diagram, the
information shown in appears in
the Context Help window. Select
Help>>Find Examples to launch the
NI Example Finder, double-click
Fundamentals, double-click Graphs
and Charts, and double-click the Waveform
Graph VI to open the example. Refer to the
lesson on Data Acquisition and
Waveforms for more information about the
waveform data type.
Save the VI as Graph Waveform Array.vi in the
C:\Exercises\LabVIEW Basics I directory.
Run the VI
Display the front panel and run the VI. The VI plots the
auto-indexed waveform array on the waveform
graph.
Enter the index of any element in the Waveform
Array index display to view the value of that
element. If you enter a number greater than the array size
of 100, the display dims.
Use the Positioning tool to resize
Waveform Array to view more than one
element. The indicator displays elements in ascending index
order, beginning with the index you entered.
Block Diagram
In this block diagram, you use the default value of the
initial x and
Δx value for the waveform. In cases where the initial
x and
Δx value are a specific value, use the
Bundle function to specify an initial
x and
Δx value for a waveform array.
Modify the block diagram as shown in .
Place the Bundle function, located on the
Functions>>All Functions>>Cluster palette,
on the block diagram. This function assembles the plot
elements into a single cluster. The elements include the
initial x value
(20), the
Δx value (0.5), and
the y array of waveform
data.
Create two numeric constants for the initial
x value and
Δx value.
Label the
Δx constant by typing Dx. Use the
Labeling tool to select the D
and select the Symbol font from the
Text Settings pull-down menu on the
toolbar. D converts to the delta symbol
(Δ).
Wire the block diagram as shown in .
Save the VI.
Run the VI
Display the front panel and run the VI. The graph displays
the same 100 points of data
with a starting value of 20
and a
Δx
of 0.5 for each point on the
x-axis. In a timed test, this graph would correspond to
50 seconds worth of data
starting at 20 seconds.
Change the initial x and
Δx
values in only one location, either the
Bundle function or in the Waveform
Graph Properties dialog box.
If time permits, complete the optional steps. Otherwise,
close the VI.
Optional
Right-click the waveform graph and select
Visible Items>>Graph Palette from the shortcut
menu to display the graph palette. Click the
Zoom button to see the data on the graph in
more detail.
Right-click the graph and select Visible Items>>Scale
Legend from the shortcut menu to display the scale
legend.
Return to the block diagram. Create a multiple-plot waveform
graph by building a 2D array of the data type normally
passed to a single-plot graph. Modify the block diagram as
shown in .
Place the Sine function, located on the
Functions>>Arithmetic & Comparison>>Express
Numeric>>Express Trigonometric palette, on the
block diagram. Use this function to build an array of
points that represents one cycle of a sine wave.
Place the Build Array function, located on
the Functions>>All Functions>>Array
palette, on the block diagram. This function creates the
data structure to plot two arrays on a waveform
graph.
Place the pi constant, located on the
Functions>>Arithmetic & Comparison>>Express
Numeric>>Express Numeric Constants palette, on
the block diagram.
Wire the block diagram as shown .
Save the VI.
Display the front panel and run the VI. The two waveforms
plot on the same waveform graph.
Display the block diagram.
Right-click the wire to Waveform Array ,
select Custom Probes>>Controls>>Graph
Indicators from the shortcut menu, and select a
waveform graph to place a graph probe on the wire.
Display the front panel and run the VI. The probe shows only
the data array. The sine wave is not present because you did
not place the probe on the wire to which the sine wave is
bundled.
Close the Probe window.
Zoom in on a portion of the graph.
Click the Zoom button on the graph palette,
shown in , to display the
Zoom pull-down menu.
Select Zoom by X Rectangle, as shown in
.
Click and drag a selection rectangle on the graph. When
you release the mouse button, the graph display zooms in
on the selected area.
You also can select Zoom by Y Rectangle
or Zoom by Selected Area. Experiment with
these options.
Select Undo Zoom from the lower left corner
of the pull-down menu to undo a zoom or click the x-axis
single fit button and the y-axis single fit button on
the scale legend, shown in and
.
Use the Panning tool, shown in , to click and drag the graph display. Click
the x-axis and y-axis single fit buttons again to restore
the display to its original position.
Use the Cursor Movement tool, shown in , to return the cursor to standard mode.
Save and close the VI.